GB1592808A

GB1592808A - Pipe connecting members

Info

Publication number: GB1592808A
Application number: GB48015/77A
Authority: GB
Original assignee: Pont a Mousson SA
Current assignee: Pont a Mousson SA
Priority date: 1976-11-22
Filing date: 1977-11-18
Publication date: 1981-07-08
Also published as: DE2752077A1; SE7712990L; NL7712788A; ES464364A1; BE861021A; FR2405122A2; CA1163657A; IT1091614B; ES464365A1; FR2405122B2

Description

(54) IMPROVEMENTS IN OR RELATING TO PIPE CONNECTING MEMBERS (71) We, PONT-A-MOUSSON S.A., a Societe anonyme organised under the laws of France, of 91, Avenue de la Liberation, 54000 Nancy, France, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to pipeconnecting devices of the type comprising a socket in which an annular gasket is fixed, the socket defining a smooth annular surface consisting of a polyolefin. These devices are used in the production of joints between pipes in which a flared end of one pipe receives a male end of another pipe, a gasket being inserted between these two pipe ends. These devices may comprise flared socket or sleeves for connecting pipes, or even rings such as protective rings having an L-shaped section, intended to be connected to flared members of this type.

The gasket may be of the radial compression type or may use lips, or even an anchoring heel portion and a rim for securing the male end connected by a flexible web. In all cases, it is subjected to an entrainment force when the male end is introduced into the flared end and to an expulsion force when operating pressure is established in the pipe. It is therefore important that the gasket is retained axially by at least one of the members constituting the joint.

The axial retaining device used most frequently hitherto consists of a radial flange of the gasket, or heel portion, which is anchored in annular groove provided in one of the two pipes. Most frequently, the radial flange is external and the annular groove is provided inside the flared socket pipe.

The provision of the annular groove for housing the flange takes place in a relatively simple manner when producing a cast iron pipe, where it is possible to use a sand core of appropriate shape which disintegrates after casting. On the other hand, the provision of a groove of this type on pipes made from plastics material is much more difficult and requires the use of very complicated mechanisms which are therefore very expensive. In any case, it is necessary to give the heel portion a certain volumetric size, which, from the strict point of view of the seal between the pipes, is absolutely useless. On the other hand, quite high dimensional accuracy is required, if it is desired that the anchoring of the heel portion in the groove is sufficiently firm and constant from one joint to another.

Furthermore, pipes made from plastics material are frequently too thin to be able to provide a groove.

French Patent 1 328 661 also discloses a method of anchoring a gasket flange consisting of clamping this flange between the end face of the flared socket and a ring connected to the latter. The latter method also requires certain dimensional accuracy to produce this anchorage and a volume of gum which has no purpose as regards the seal, is also used in the axial gripping of the flange. In addition, this excludes a simple securing operation, for example by the interlocking of parts of low relief of the ring, owing to the considerable axial force, due to clamping of the flange, which this anchorage must withstand.

Methods of attachment by sticking the gasket to the socket are also known. The latter represent very long and therefore expensive additional work and raises problems of compatibility of the adhesives firstly with the rubber gasket and secondly with the pipeconnecting member receiving the latter, which problems are not always easy to solve: for example, if the piping is made of plastics material, it is necessary to find adhesives which are effective both as regards plastics material and rubber without attacking either the plastics material or the rubber.

The invention therefore intends to resolve this problem of the axial retention of a gasket in a manner which does not involve the above drawbacks.

According to the present invention, there is provided a pipe-connecting device of the type comprising a socket at least a part of which is fabricated from polyolefin and an annular gasket fixed to the socket, characterised in that the gasket is made from ethylene-propylene-dienemethylene rubber vulcanized with sulphur or with a substance producing sulphur and has a smooth annular surface welded to a corresponding smooth annular polyolefin surface of the socket.

The invention also relates to a method for the manufacture of such a pipe-connecting member. In a first method, the smooth surface of the gasket is cleaned, the two smooth surfaces are heated to similar temperatures, the smooth polyolefin surface being heated to the temperature at which it softens, and these two smooth surfaces arc placed one against the other.

In a second method, the smooth surface of the gasket is cleaned, this gasket is placed in a mould, and the polyolefin of the socket is moulded using the gasket as an insert.

Further features and advantages of the invention will become apparent from ensuing description, given as a non-limiting example and with reference to the accompanying drawings in which: Figure 1 is a half view of diametral section of a pipe-connecting member according to the invention; Figure 2 is a similar half view of a joint produced by means of this member; Figures 3, 5, 7 and 4, 6, 8 are half views corresponding firstly to figure 1, secondly to figure 2, of other embodiments of the invention; Figures 9 and 10 are half views in axial section respectively illustrating two stages of the welding of the heel portion for radial anchorage of a gasket to the end face of a socket by means of a device according to the invention; Figure 11 is a half view in axial section of the pipe-connecting member produced in this way; In a manner similar to figures 9 and 10, figures 12 and 13 illustrate two stages of the welding along two surfaces of a gasket to a socket by means of another embodiment of the device according to the invention Figure 14 is a half view in axial section of another embodiment of the device according to the invention, for welding a gasket and socket along frustoconical surfaces; and Figure 15 is a half view in axial section of the gasket and the socket welded by means of the device of figure 14.

Each of figures 1, 3, 5 and 7 show a rubber gasket connected to a pipe-connecting member used to produce a joint.

The gasket is moulded and vulcanized in one piece from an ethylene-propylenediene-methylene mixture, with sulphur or a substance producing sulphur such as a mercaptan. The member to which this gasket is fixed is moulded from polypropylene.

In figures 1, this polypropylene member is a ring B having an L-shaped section. This ring comprises a cylindrical skirt 2 and an inner radial flange 3. The skirt 2 is intended to cover, over a part of its length, the flared end 4 of a pipe and to be retained therein by the clipping or engagement of an inner semi-annular continuous or non-continuous bead 5 in a corresponding groove 6 in the outer wall of the flared end 4. The ring B and flared end 4 together form a socket of the device. To facilitate positioning of the ring B, an inner chamfer 7 is provided at the end of the skirt 2 remote from the flange 3.

The flared end 4 may in particular terminate a pipe or sleeve for connecting pipes and when in operation it receives the male end 8 of a second pipe.

The flange 3 is defined by two plane radial surfaces, one outer surface 9 and another inner surface 10. The gasket G is fixed to the latter surface under the conditions described hereafter. The flange 3 is defined internally, internally meaning radially inwardly, by a conical surface 11 which assists guidance of the smooth end at the time of its introduction into the socket. The nose 12 located at the corner of the inner conical surface 11 and of the radial plane surface 10 of the flange 3 has an inner diameter slightly greater than the outer diameter d of the male end, in order to contribute to centering the latter in the flared end 4 for the purpose of ensuring correct operation of the joint over its entire periphery.

The gasket G essentially comprises three parts, which are respectively a heel portion 13, an intermediate part 14 and an active part 15.

The heel portion 13 is the part of the gasket G by which the latter is connected to the radial surface 10 of the ring B. This heel portion is radial and has a constant depth.

The outer cylindrical surface 16 which limits the latter radially has a diameter slightly less than the inner diameter of the skirt 2. The depth of the heel portion 13 is just sufficient, taking into account the characteristics of tensile strength of the rubber constituting the gasket G, to withstand tearing in the region of the connection between this heel portion and the part 14 described hereafter.

Furthermore, this depth is such that, when the ring B is engaged on the flared part 4, the heel portion 13 is not clamped between the side 10 and the end face of the flared part 4.

The part 14 of the gasket G is cylindrical and is connected to the inner end of the heel portion 13. The diameter of its outer cylindrical surface 17 is approximately equal to the inner diameter D of the flared end 4; the diameter of its inner cylindrical surface 18 is slightly greater than that d the outer surface of the smooth end 8, in order to centre this smooth end under the same conditions as provided by the nose 12.

The salient angle between the heel portion 13 and the cylindrical part 14 is reduced by a chamfer 19 (figure 2).

The part 15 of the gasket G is the active part, i.e. that which ensures the seal of the joint. To this end, its depth is calculated to satisfy the requirements of radial compression between the flared part 4 and the smooth end 8 after the introduction of the latter, that is to say that it is greater than the half difference D-d. In addition, at the end remote from the heel portion 13, this active part 15 is provided with two divergent lips 20 which the operating pressure established in the pipe presses against the flared part 4 and against the smooth end 8 respectively. This part 15 has a general frustoconical shape diverging towards the outside of the joint, i.e. towards the heel portion 13. This inclination, in association with the chamfer 7, assists positioning of the arrangement of the ring B and gasket G, which has a U-shaped section, on the flared part 4.

Figure 2 shows the joint completely assembled, with not only the ring B and the gasket G fixed to the flared part 4 by clipping 5 in 6, but also with the smooth end 8 introduced into the flared end 4.

The area of contact between the flange 3 of the ring B and the heel portion 13 of the gasket G is illustrated with shading. This connection is achieved with heating under the following conditions. The gasket G, moulded and vulcanized from the aforementioned mixture in the presence of a stripping agent such as silicone, firstly undergoes cleaning of its outer radial face 13a by means of a solvent for the stripping agent and wax which sweats on the surface of the rubber. This solvent may be acetone, petrol or methyl alcohol for example. Then1 this bare gasket, i.e. devoid of any coating, is positioned in the injection mould for the ring B in order to fulfil the function of an insert. Injection of the polypropylene is then undertaken, after closure of the mould on its insert.

It is also possible to achieve connection of the heel portion 13 to the flange 3, still with heating, by using the technique of so-called "mirror welding" described with the apparatus suitable for obtaining end-to-end welding in the said French Patent 1183 622.

In this case, the faces 10 and 13a are simultaneously pressed against the two faces of a heating plate. When the face 10 softens, the heating plate is removed and the faces 10 and 13a are pressed one against the other. Heating of the rubber serves to eliminate sudden cooling of the polypropylene during this pressing operation and the formation of a solid film hindering the connection of the two materials. Beads of plastics material which are formed at the higher temperature are housed between the surface 16 and the skirt 2 and in the space provided by the chamfer 19.

In the two methods of connection, it will be seen that the faces 10 and 13a are surprisingly connected directly in a very rigid manner: if traction is exerted on the gasket, these faces do not separate, but the rubber tears internally. It is thought that the solid connection achieved is due to the creation of bridges between the two materials caused by the presence of residual sulphur in the vulcanized rubber.

In the method of connection by moulding, the molten polypropylene comes in contact with the uncleaned cylindrical surface 16 of the heel portion 13. It is thus possible for a connection to be produced which is more or less extensive and more or less solid at this point, which is not troublesome. In addition, for reasons of economy, if one wishes to use a simple nonretractable moulding core, it is preferable not to provide a chamfer 19, since the space provided by this chamfer would be filled with plastics material at the time of moulding, which would form a hard and fragile "point" at this location. On the other hand, in the following examples where the gasket is fixed directly to the flared part 4, the chamfer 19 is very desirable, since, without having this drawback, it is the latter which ensures guidance and centering of the male end 8.

Figure 3 shows a variation of the invention in which the heel portion 13 and more precisely its radial face 13b opposite the face 13a is welded against the end face 21 of the flared part 4 by one of the two methods which have just been described. In this case, if one uses the technique of "mirror welding", it is once more recommended to give the active part 15 of the gasket G a general frustoconical shape in order that the flared part 4 is able to be housed easily against the shoulder constituted by the heel portion 13 of the gasket. Figure 4 shows the joint in the assembled state, with only the active part 15 compressed radially between the smooth end 8 and the flared part 4, with its lips 20 able to be pressed against the smooth end and the flared part by pressure, as previously.

On the other hand, if the assembly of the gasket G and flared part 4 is produced by direct moulding of the flared part on the insert constituted by the gasket, there is no longer any relative sliding to take place between the polypropylene of the flared part and the rubber of the gasket; the active part of the latter may thus have a general cylindrical shape, like the intermediate part 14. This configuration is shown in figures 5 and 6. In this case, the connection naturally involves both the end face 21 of the flared part and its inner surface 22, but the connection is absolutely reliable solely on the surfaces of the gasket cleaned prior to moulding of the flared part.

Figure 7 shows another variation in which the gasket G' does not comprise a heel portion, but has a completely cylindrical outer surface 23. Connection may take place by moulding the flared part on the insert constituted by the gasket G', after cleaning the surface 23. In this case, as in the preceding example, the active part of the gasket may be cylindrical, since there is no relative movement of the flared part with respect to this gasket.

It is also possible to envisage "mirror" welding in the following manner: the diameter of the surface 23 is chosen to be slightly less than the diameter D. A cylindrical or frustoconical split heating ring is placed between the gasket and the flared part, suitably positioned axially. When the inner surface of the flared part becomes soft, this ring is withdrawn and one brings about expansion of the gasket, for example by means of an inflatable inner tube. In this case, it is desirable that the active part of the gasket has a frustoconical shape, as shown in figure 7.

Owing to the usefulness of a ring for centering the male end 8 and protecting the joint from dust and other foreign bodies, it is naturally possible to attach a ring B' of this type to the joints of figures 3 to 8, as shown in dot-dash lines in figures 7 and 8.

It should be noted that in all the examples mentioned, where the gasket acts by radial compression between the flared part and the male end or by the application of its two terminal lips against these two parts, connection with heating of the gasket to the relative surface of the socket may be imperfect, without this impairing the seal. It is sufficient if this connection is solid enough to counterbalance the axial forces exerted on the gasket, which is the case.

However, it has been found that subject to certain operating precautions, direct welding carried out in this way may be made sufficiently reliable to ensure a seal on its own. It is thus possible to use the latter to ensure direct connection and the seal of the heel portion of a gasket in a flared part, the gasket comprising at its other end, a bead securing the smooth end, separated from the flared part and connected to the heel portion by a flexible web.

The joints produced according to the invention are very advantageous: connection by direct welding uses very little gum for its attachment, since the heel portion 13 may be reduced to just the film necessary for being connected at the chosen point and successfully retaining the gasket against axial forces. Possibly, this heel portion may even be eliminated.

A very small surface is sufficient for the connection. Cleaning of the remainder of the gasket is superfluous.

Thus, no glueing of the gasket is necessary, nor any groove in the flared part.

Welding takes place very efficiently even with large tolerances on the two connected parts.

It has been found that the same methods of direct welding were suitable when the ring B or flared part 4 consisted of another polyolefin, in particular polyethylene. In addition, it is also possible to use the invention for producing a joint between pipes of other material: as indicated in dotdash lines in figures 3 and 4, it is possible to deposit a layer 24 of polyolefin on the end face of the flared part, then to carry out mirror welding of the heel portion of the gasket to this layer. It is thus possible to achieve a connection of the gasket and cylinder 25 of polyolefin, by one of the two methods and to fix the latter to the end of the flared part (dot-dash lines in figures 5 and 6). It is also possible to deposit a tubular layer 26 of polyolefin on the inner surface of the flared part (dot-dash lines in figures 7 and 8) and to carry out mirror welding of a cylindrical gasket G' on this layer. These variations make it possible to secure a gasket to cast iron pipes comprising a smooth socket and thus to simplify the core and casting of the latter.

The example of figures 9 to 11 illustrates the welding of a gasket 31 of rubber and a socket 32 of thermoplastic plastics material.

The gasket 31 is made from rubber based on ethylene - propylene - dienemethylene vulcanized with sulphur. The socket 32 is for example the flared end of a connecting sleeve made of a polyolefin, in particular polypropylene. More generally, the socket 32 forms part of a tubular member used to form a joint between pipes. It may be an integral part of this tubular member and constitute the flared socket of the latter, or may be set into this member, which may thus consist of a different material not suitable for welding: temperature or thermosetting plastics material, asbestos cement, sandstone etc.

The socket 32 has a smooth inner cylindrical surface 33 comprisng a radial end face 34.

The gasket 31 essentially comprises three parts, which are respectively a heel portion 35, an intermediate body 36 and an active part 37.

The heel portion 35 is the part of the gasket 31 by which the latter is connected to the radial surface 34 of the socket 32. This heel portion is radial and of constant thickness. It is limited radially by an outer cylindrical surface 38 and has inner and outer diameters equal to the corresponding diameters of the socket 32. On accound of the characteristics of tensile strength of the rubber constituting the gasket 31, the axial depth of the heel portion 35 is just sufficient to withstand tearing in the region of the connection between this heel portion and the part 36 described hereafter.

The body 36 of the gasket 31 is cylindrical and connected to the inner end of the heel portion 35. The diameter of its outer cylindrical surface 39 is approximately equal to the inner diameter D of the socket 32. The diameter of its inner cylindrical surface 40 is slightly greater than that of the outer surface of the smooth end (not shown) intended to be introduced into the socket, in order to centre this smooth end. The salient angle between the heel portion 35 and the cylindrical'body 36 is reduced by a chamfer 41.

The part 37 of the gasket 31 is the active part, i.e. the part which ensures the seal of the joint. To this end, its depth is calculated to satisfy the requirements of radial compression between the socket 32 and the smooth end after introduction of the latter.

In addition, opposite the heel portion 35, this active part 37 is provided with two divergent lips 42 which the operating pressure established in the pipe presses respectively against the surface of the socket and against the smooth end. This part 37 has a general frustoconical shape diverging towards the outside of the joint, i.e. towards the heel portion 35. This inclination, association with the chamfer 37, facilitates positioning of the gasket 31 in the socket at the time of welding.

In this example, the gasket 31 is intended to be fixed to the socket 32 by welding of the end face 34 of the socket and the corresponding radial face 43 of the heel portion 35, which is adjacent the outer peripheral surface 39 of the body 36 of the gasket.

To this end, one uses a device D' which consists of a heating ring 44, for example of copper or a copper alloy, provided with an embedded electrical heating resistance 45 supplied with current through a two-wire lead 46. Preferably, the ring 44 is coated with an anti-adherent layer, such as for example a film of polytetrafluouroethylene (PTFE) or other fluorinated substance for the purpose of preventing sticking of the plastics material to the ring.

The ring 44 is flat and comprises two parallel heating faces 47, 48 whereof the inner diameter and outer diameter corresponds respectively to the inner and outer diameter of the heel portion 35 and the end face 34 of the socket 32. The ring 44 is integral with an insulating handle 49. As a variation, the electrical resistance could be eliminated and the device D' could be heated by means of a burner or any other appropriate means.

To effect welding, the gasket 31, the device D1 and the socket are aligned axially in this order along the axis X-X of the socket 32 (Fig. 9), after having prepared the surfaces to be welded as necessary. This preparation consists of cleaning the surfaces. In particular, the surface 43 of the gasket is cleaned by means of a solvent for the agent for stripping rubber (for example silicone) and wax which sweats on the surface of the rubber. Then, these members are moved together and the gasket 31 is introduced inside the socket 32, the surface 39 of the body 36 fitting on the inner surface 33 and the face 43 of the heel portion 35 and the end face 34 are brought into contact with the ring 44 of the device D' (Fig. 10).

The device D' is heated to the appropriate temperature, of the order of 250"C, until one obtains softening of the end face 34, which takes about 30 seconds. The rubber of the gasket 31 is heated simultaneously, but does not soften. The gasket is then moved quickly away from the socket in order to completely release the device D', as shown in figure 9, then this device is quickly withdrawn and the gasket 31 is introduced quickly into the socket until the hot heel portion 35 comes into contact with the softened surface of the end face 34 of the socket 32. This contact is maintained for several moments (approximately 30 seconds), until the end of the socket solidifies. This is sufficient to guarantee a perfect weld leaving the body 36 and the lips 42 of the gasket 31 free.

Heating of the rubber serves to eliminate sudden cooling of the polypropylene when pressed against the latter and the formation of a solid film preventing connection of the two materials.

Surprisingly, it has been found that the two faces 43 and 34 are connected directly in a very solid manner: if one pulls on the gasket, these faces do not separate, it is the rubber which tears internally.

By way of a variation, the handle could be directed radially towards the inside in order to facilitate welding of the outer radial face 43' of the heel portion to an inner flange of a ring intended to cover a flared socket, as shown in figures 1 and 2.

The example of figures 12 and 13 illustrates welding of the same gasket 31 and the same socket 32. However, instead of being limited to the heel portion 35 and the end face 34, welding is extended to a part of the inner surface 33 and to the peripheral surface 39 of the body 36 of the gasket (Fig.

13), however, leaving the lips 42 of the gasket free.

The device D2 used for effecting this welding, firstly comprises a heating tool constituted by a ring in one piece 50 having a right-angled or L-shaped meridian section.

An L-shaped heating resistance 51 supplied with current by the two-wire circuit 46 is embedded in the ring 50 and only the inner faces of the L are used for heating. One side 52 of the right-angle constituted by a part in the form of a flat ring is intended for heating the end face 34. The other side 53 of the right-angle is constituted by a thin cylindrical ring and is intended for heating the smooth inner cylindrical surface 33 of the socket 32. The inner surfaces of the right-angle fit exactly on the respective surfaces which they heat. In order to heat the two surfaces 43 and 39 of the gasket, it is possible to use a second similar, but not identical device D2, whereof the outer dimensions of the L are adapted to these two surfaces. But it is also possible to provide only one device D2 for the socket 32, the gasket being heated in an appropriate bath or in an oven.

This heating tool is combined with a cold metal ring 54 for gauging the outer diameter of the socket 32. The inner surface of the ring 54, which is cylindrical and smooth like the outer surface of the socket 32, is fitted on the end of the latter for the purpose of controlling its expansion due to heating by means of the ring 50 and of forcing the latter to preserve a dimension which facilitates its connection to the gasket 31 which does not itself expand in the same manner.

To carry out welding of the gasket 31 in the socket by means of ring 50 and 54, one preceeds in the following manner (Figs. 12 and 13): After having prepared the faces to be welded as previously, the cold ring 54 is fitted on the socket, outside the latter, such that the two end faces are substantially coplanar and the ring 50 is introduced into the socket. The ring 50 is heated to the said temperature of the order of 250"C until the surfaces 33 and 34 to be welded soften, which takes approximately 30 seconds, when the depth of the socket 32 is of the order of 3 millimetres. The gasket 31 is heated simultaneously. Then the ring 50 is withdrawn quickly and the hot gasket 31 is introduced into the socket, in its final position for obtaining a seal by exerting and maintaining contact with slight pressure of the heel portion 35 against the end face 34 and the body 36 against the smooth inner surface 33 and this is for several moments, until cooling and re-solidification of the plastics material.

Contact under pressure may be obtained by means of a tool 55 providing axial and radial pressure of the type of the stopper of a thermos flask' '('Fig. 43). This tool 55 comprises, around a cylindrical support core 56 having an outer screwthread 57 and terminal radial flange 58, a flange 59 abutting axially against the anchoring heel portion 35 of the gasket 31, mounted loosely on the screwthread 57 and an intermediate resilient sealing washer 60 which can be expanded or inflated radially by moving the flange 59 and flange 58 together under the action of a tightening nut 61 screwed onto the screwthread 57. It is the radial expansion of the washer 60 which ensures radial pressure of the body 36 of the gasket against the surface 33 of the socket. As regards the axial pressure, it is exerted by the operator on the tool 55. The dimensions of the parts of this tool are naturally adapted to those of the two members to be welded.

Perfect welding of the gasket 31 in the socket 32 is thus obtained, still leaving the lips 42 of the gasket free.

The same principle may also be applied (figures 14 and 15) to the welding of a gasket 3 lea of the radial compression type comprising for example an abutment heel portion 35a having radial faces 43a, a body 36a with a frus roughly in the form of a parallelogram. An electrical heating resistance 66 of appropriate shape is embedded in the ring 63 and supplied with current through a twowire circuit 46. A handle 67 serves for handling the heating ring 63.

The heating ring 63 is combined as previously with a cold metal ring 54 for gauging the end of the socket 32a.

To effect welding of the gasket 31 a to the socket 32a, one proceeds in the following manner: As previously, the end of the socket is covered with the cold gauging ring 54. The heating ring 63 is brought into contact with the frustoconical surface 62 and the end face 34a along the axis X-X of the socket.

Then the gasket 31a is moved closer coaxially and placed in contact with the heating ring 63 by the inner face 43a of its heel portion 35a and the frustoconical peripheral surface 39a of its body 36a (Fig.

14).

An electrical current is passed through the resistance 66 until the end face 34a and the flared inlet 62 of the socket becomes soft. When this softening is achieved, the gasket 31a is removed quickly, the heating ring 63 is withdrawn quickly and the gasket 31a is rapidly replaced at the entrance to the socket, in contact by its surfaces 43a and 39a with the end face 34a and the frustoconical inlet surface 62 of the latter, with slight axial pressure (Fig. 15). The contact is maintained for the time necessary for re-solidification of the plastics material.

One thus obtains perfect welding of the gasket 31a and the socket along the surfaces indicated, leaving the sealing bead 37a free.

As a variation, it is possible to envisage using a single oblique heating face 64 of the ring 63, for softening the surface 62, the gasket 31a for being heated by other means such as a bath or oven. In this case, the section of the ring 63 may be different from that illustrated, for example triangular.

There would naturally be obtained in a similar manner, a weld of a gasket comprising a bead 37a and outer frustoconical surface, but without a heel portion 35a, the weld thus taking place solely along the surfaces 39a and 62.

As a variation, in certain applications, instead of being produced in the form of a complete ring, the heating rings 44, 50 and 53 may be constituted by a split ring, i.e.

extend along an arc of a circle slightly less than 360" in order to have a certain elasticity. They may also be made in the form of two plvoted or independent half rings.

These variations may facilitate positioning and removal of the heating rings.

WHAT WE CLAIM IS: 1. A pipe-connecting device of the type comprising a socket at least a part of which is fabricated from polyolefin and an annular gasket fixed to the socket, characterised in that the gasket is made from ethylenepropylene-diene-methylene rubber vulcanized with sulphur or with a substance producing sulphur and has a smooth annular surface welded to a corresponding smooth annular polyolefin surface of the socket.

2. A pipe-connecting device according to claim 1, comprising a polyolefin ring intended to be connected to a flared end of a pipe section to define said socket with the flared pipe end, characterised in that the smooth surface of the gasket is formed on a radial heel poition thereof and is welded to a radial face of the ring.

3. A pipe-connecting device according to claim 2, characterised in that the ring and the flared pipe end are provided with complementary interlocking members arranged such that, when they co-operate, a gap whose thickness is equal at least to the thickness of said heel portion is defined between said radial face of the ring and an end face of the flared pipe end.

4. A pipe-connecting device according to claim 1, comprising a polyolefin pipe section having a flared end defining said socket, characterised in that the smooth surface of the gasket is formed on a radial heel portion thereof and is welded to an end face of the flared end.

5. A pipe-connecting device according to claim 4, characterised in that the gasket has a second smooth surface which is cylindrical and welded directly to a second inner smooth surface of the flared pipe end.

6. A pipe-connecting device according to claim 1, characterised in that the two smooth annular surfaces are frustoconical.

7. A pipe-connecting device according to claim 6, characterised in that the gasket has a second smooth annular surface which is radial and welded to a radial second smooth annular surface of polyolefin defined by the socket.

8. A pipe-connecting device according to claim 1, comprising a terminal flared end of a polyolefin pipe section defining said socket, characterised in that the gasket is generally cylindrical and comprises no heel portion and in that said smooth surfaces are respectively the outer surface of the gasket and the inner surface of the flared pipe end.

9. A pipe-connecting device according to any one of claims I to 7, characterised in that the gasket has an active part spaced radially from the smooth surface of the socket.

10. A pipe-connecting device according to any one of claims 1 to 9, characterised in that the smooth surface of the socket is defined by polyolefin material set into the end of a pipe element.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

roughly in the form of a parallelogram. An electrical heating resistance 66 of appropriate shape is embedded in the ring 63 and supplied with current through a twowire circuit 46. A handle 67 serves for handling the heating ring 63.

The heating ring 63 is combined as previously with a cold metal ring 54 for gauging the end of the socket 32a.

To effect welding of the gasket 31 a to the socket 32a, one proceeds in the following manner: As previously, the end of the socket is covered with the cold gauging ring 54. The heating ring 63 is brought into contact with the frustoconical surface 62 and the end face 34a along the axis X-X of the socket.

Then the gasket 31a is moved closer coaxially and placed in contact with the heating ring 63 by the inner face 43a of its heel portion 35a and the frustoconical peripheral surface 39a of its body 36a (Fig.

14).

An electrical current is passed through the resistance 66 until the end face 34a and the flared inlet 62 of the socket becomes soft. When this softening is achieved, the gasket 31a is removed quickly, the heating ring 63 is withdrawn quickly and the gasket 31a is rapidly replaced at the entrance to the socket, in contact by its surfaces 43a and 39a with the end face 34a and the frustoconical inlet surface 62 of the latter, with slight axial pressure (Fig. 15). The contact is maintained for the time necessary for re-solidification of the plastics material.

One thus obtains perfect welding of the gasket 31a and the socket along the surfaces indicated, leaving the sealing bead 37a free.

As a variation, it is possible to envisage using a single oblique heating face 64 of the ring 63, for softening the surface 62, the gasket 31a for being heated by other means such as a bath or oven. In this case, the section of the ring 63 may be different from that illustrated, for example triangular.

There would naturally be obtained in a similar manner, a weld of a gasket comprising a bead 37a and outer frustoconical surface, but without a heel portion 35a, the weld thus taking place solely along the surfaces 39a and 62.

As a variation, in certain applications, instead of being produced in the form of a complete ring, the heating rings 44, 50 and 53 may be constituted by a split ring, i.e.

extend along an arc of a circle slightly less than 360" in order to have a certain elasticity. They may also be made in the form of two plvoted or independent half rings.

These variations may facilitate positioning and removal of the heating rings.

WHAT WE CLAIM IS: 1. A pipe-connecting device of the type comprising a socket at least a part of which is fabricated from polyolefin and an annular gasket fixed to the socket, characterised in that the gasket is made from ethylenepropylene-diene-methylene rubber vulcanized with sulphur or with a substance producing sulphur and has a smooth annular surface welded to a corresponding smooth annular polyolefin surface of the socket.
2. A pipe-connecting device according to claim 1, comprising a polyolefin ring intended to be connected to a flared end of a pipe section to define said socket with the flared pipe end, characterised in that the smooth surface of the gasket is formed on a radial heel poition thereof and is welded to a radial face of the ring.
3. A pipe-connecting device according to claim 2, characterised in that the ring and the flared pipe end are provided with complementary interlocking members arranged such that, when they co-operate, a gap whose thickness is equal at least to the thickness of said heel portion is defined between said radial face of the ring and an end face of the flared pipe end.
4. A pipe-connecting device according to claim 1, comprising a polyolefin pipe section having a flared end defining said socket, characterised in that the smooth surface of the gasket is formed on a radial heel portion thereof and is welded to an end face of the flared end.
5. A pipe-connecting device according to claim 4, characterised in that the gasket has a second smooth surface which is cylindrical and welded directly to a second inner smooth surface of the flared pipe end.
6. A pipe-connecting device according to claim 1, characterised in that the two smooth annular surfaces are frustoconical.
7. A pipe-connecting device according to claim 6, characterised in that the gasket has a second smooth annular surface which is radial and welded to a radial second smooth annular surface of polyolefin defined by the socket.
8. A pipe-connecting device according to claim 1, comprising a terminal flared end of a polyolefin pipe section defining said socket, characterised in that the gasket is generally cylindrical and comprises no heel portion and in that said smooth surfaces are respectively the outer surface of the gasket and the inner surface of the flared pipe end.
9. A pipe-connecting device according to any one of claims I to 7, characterised in that the gasket has an active part spaced radially from the smooth surface of the socket.
10. A pipe-connecting device according to any one of claims 1 to 9, characterised in that the smooth surface of the socket is defined by polyolefin material set into the end of a pipe element.
11. A method for the manufacture of a

pipe-connecting device according to any one of claims 1 to 10, characterised in that the smooth surface of the gasket is cleaned, the two smooth surfaces are heated to similar temperatures, the smooth polyolefin surface is heated to the temperature at which it softens, and the two smooth surfaces are pressed one against the other.
12. A method according to claim 11, characterised in that the two smooth surfaces are heated by pressing them simultaneously against two faces of a heating member of corresponding shape until the polyolefin softens, and the heating member is then withdrawn and the two smooth surfaces are pressed one against the other.
13. A method according to claim 12, characterised in that the two smooth surfaces are cylindrical and the surface of the gasket is pressed against the other surface by means of an inflatable tubular chamber.
14. A method for the manufacture of a pipe-connecting device according to any one of claims 1 to 10, characterised in that the smooth surface of the gasket is cleaned, the gasket is positioned in a mould, and the polyolefin of the socket is moulded using the gasket as an insert.
15. A method according to any one of claims 11 to 14, characterised in that the smooth surface of the gasket is cleaned by means of a solvent for the stripping agent and wax which sweats on the surface of the rubber.
16. A pipe-connecting device substantially as hereinbefore defined with reference to the accompanying drawings.
17. A method for the manufacture of a pipe-connecting device according to any one of claims 1 to 10, substantially as hereinbefore defined with reference to the accompanying drawings.